When running the program, you have to select one of menu items from "Tools->Log file" in order to view or truncate your Log file. The log file contains the detailed description of any errors and other events that occurred while processing script.
Default log file location is product's directory and the name is ERROR.LOG. When the user has no enough permissions DTM Data Generator for JSON saves log to typical path like C:\Documents and Settings\<username>\Application Data\dgjson.log or C:\Users\<username>\AppData\Roaming\dgjson.log
The log file is a text file that contains three type of records: